1. Field of the Invention
The application relates to a method and apparatus utilized in a wireless communication system, and more particularly, to a method and apparatus of performing direct communications in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (CoMP), uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Please refer to FIG. 1, which is a schematic diagram of a wireless communication system 10 according to the prior art. The wireless communication system includes a network 100 and two communication devices 102 and 104. The network can be an E-UTRAN and the communication devices 102 and 104 can be UEs. In detail, when the communication device 102 needs to transmit data to the communication device 104, the communication device 102 sends data via the network 100 and the communication device 104 receives data via the network 100. In other words, the network 100 receives data from the communication device 102 and transmits data to the communication device 104. This is similar forwarding. This forwarding is unnecessary and wastes overhead due to the reception and transmission. If the communication device 102 can directly transmit data to the communication device 104, the overhead can be saved by avoiding this forwarding. However, how to realize direct communications between two communication devices is not defined in the prior art.